Demand for increased functionality and performance of integrated circuits has driven designs to extremely high integration density of electronic elements therein that are scaled to extremely small feature sizes. High integration density allows more electronic elements to be provided on a semiconductor chip of a given size while small size and close proximity of those electronic elements reduces signal propagation time, allowing higher clock speeds, and noise susceptibility. Many sophisticated structures have been designed and exotic materials employed to maintain adequate electrical operating margins for transistors and field effect transistors, in particular, as transistors have been scaled to such extremely small sizes.
Among such sophisticated designs and exotic materials is the use of high dielectric constant (Hi-K) materials that have a dielectric constant of eight or greater for extremely thin gate insulators in field effect transistors. Such structures allow the geometry of the electric field and carrier concentration profiles within the conduction channel of such transistors to be controlled more accurately in order to maintain a useable ratio of resistance between “on” and “off” states of the transistors, often referred to simply as the on/off ratio. However, such materials have a high sensitivity to contamination, particularly by oxygen.
Contamination of Hi-K materials by oxygen is particularly problematic since oxygen contamination, in which oxygen diffuses into vacancies in the Hi-K material, alters the work function of the gate and causes a shift in the switching threshold of the transistor. Switching thresholds are, in turn, highly critical in integrated circuits, particularly at high switching speeds and low operating voltages, to insure that transistors change states at substantially the same instant throughout the integrated circuit. Unfortunately, many commonly required structures in integrated circuits, such as insulators or isolation structures are formed of oxides or otherwise provide a source of oxygen that can contaminate Hi-K materials during manufacture and/or operation due to thermal diffusion. Of particular concern is the fact that thermal diffusion of oxygen can continue after an integrated circuit is placed in service and degrade performance beyond specifications that were originally met.